Ophthalmic lenses are those that are used in spectacles, for either outdoor or indoor use, typically providing corrective vision for wearers to accommodate for physiological errors in the human eye, but also being plano and being for aesthetic, protective or fashion purposes. Ophthalmic lenses for outdoor use, usually referred to as sunglass lenses, have traditionally been uniformly tinted so as to reduce glare and light transmission for the comfort of the wearer. However, these lenses indiscriminately filter all light whether it is horizontally polarized or vertically polarized—glare is dampened, but not eliminated. More importantly, by filtering all components of light, visual acuity is diminished.
Light is made up of waves traveling in different directions. Vertically polarized light is useful to the human eye, however horizontally polarized light commonly exists in higher proportions as glare. Glare is concentrated light reflecting off a horizontal shiny surface, such as a car windscreen, sand, water, snow or asphalt roads, which reduces visibility and can make it uncomfortable, painful or even dangerous to carry on driving, cycling, skiing, et cetera. Accordingly, polarized ophthalmic lenses were developed for outdoor use that allow the vertically polarized component of light, which is preferred for clear vision, while eliminating the easily scattered and skewed horizontally polarized component of light. Vertically aligned light is preferred because it respects the natural tendency of the visual system to focus on the vertical component of an image.
Typically, polarized ophthalmic lenses include linear polarized filters that utilise aligned dichroic dyes to extinguish the horizontal component of reflected sunlight. In this respect, the components of light that are aligned with the axis of the polarizer are absorbed, allowing only the light oscillating with a wave aligned perpendicular to the axis of the polarizer to pass through the filter.
More recently, popularity and use of smartphones, tablets, laptops, and other devices with polarized displays is increasing. As explained in U.S. Pat. No. 7,374,282 (Robert K. Tendler), hereafter “Tendler”, when such polarized displays are viewed with an opposite or crossed orientation through an ophthalmic lens with uniform polarization (being a lens with the same degree of polarization across the entire extent of the lens), the display will appear black due to the cross-polarization effect and will not be viewable.
In that same United States patent, Tendler therefore proposes the use of a polarization gradient across the extent of a lens, such that a distant scene can be viewed through a polarized region (an upper region) of the lens, and a near scene can be viewed through a non-polarized region (a lower region) of the lens, there being either a sharp boundary between the two polarized regions or a variation in polarization from the polarized region to the non-polarized region to avoid the presence of such a sharp boundary. In Tendler, such a lens is suggested for use in sunglasses, with traditional uniform tinting across the lens, but also for use in transparent (untinted) spectacles. Tendler suggests the use of methods such as the stretching of polarization layers, or the provision of adjacent stripes of polarization material of different polarization densities, to achieve the desired gradient polarization.
A subsequent suggestion (see United States patent application publication 2015/0253465 to Giorgio Trapani and Robert K. Tendler, hereafter “Trapani et al”), for a method for producing ophthalmic lenses with a gradient characteristic is to provide a film that has a printable layer (exemplified as a layer of mordant), and to print upon that film a pattern of dots (of predetermined and varying density) with an inkjet printer to thereby provide across the extent of the film a smoothly varying gradient. In this document, gradient characteristics said to be achievable by the method are polarization, transmission and color. Indeed, in order to produce sunglass lenses, Trapani et al suggests incorporating suitable dyes into the printing so as to provide a light transmission gradient across the lens, producing sunglasses having lenses of the type that can be seen in FIG. 1 of Trapani et al, which are said to beneficially provide very little blockage of light when viewed through the lower region of the lens.
Due to the inherent light extinguishing properties of polarized filters in lenses, where one component of light that is aligned parallel with the axis of the polarizer is removed, such gradient polarized lenses, with or without the addition of tint, typically exhibit the type of varying light transmission characteristics across the lens as are described and illustrated in Trapani et al. From an aesthetic point of view, these lenses will appear to have a varying tint across the lens (again, with or without there being an added tint), and from a performance point of view, their ability to function as sunglasses is restricted. Such gradient tints are usually considered more as fashion sunglasses and wearers still experience high levels of transmitted light through the bottom (untinted) portion of the lens.